Decoding tends to be the focal point during the initial period of learning how to read because children need to be able to recognize and decode the words they encounter. Instruction is strategic as children are guided to use a variety of strategies when they encounter an unknown word.
Fluency relates to the ability to read smoothly, with few errors, and with expression. Once children have learned how to decode and recognize words quickly, they are able to practice reading fluency. When a listener can comprehend a story that has been read aloud to them by someone else as well as (or better) then they would have by reading it to themselves, the reader is fluent. This is evidenced when adults read aloud to children and children understand better than when they read it to themselves. This is because the adult is demonstrating good fluency.
Comprehension is the ability to understand what we read. There are two basic levels of reading comprehension: Literal & Inferential.
Literal comprehension is straightforward. Young readers develop understanding at the literal level first. They can recall the characters, setting, plot (or main events), and conclusion. The lower level texts have a simple plot structure, making them fairly easy to retell and comprehend at a basic level. As the level of text goes up, the text become more complex and comprehension begins to extend beyond the literal level. This is when comprehension becomes inferential. At this deeper level of comprehension, readers consider things that are not explicitly stated in the text. They think beyond the text when they wonder about the character's feelings & actions. Higher level comprehension occurs when readers think and wonder while they read. When readers ask questions, infer, draw conclusions, consider the author's purpose, and visualize their comprehension goes beyond what the text actually says and becomes reflective and thoughtful. This is the ultimate goal of reading.